This competing renewal application builds upon the success of our project Relationship Factors and HIV Treatment Adherence (R01NR010187) also known as the Duo Project. The parent grant has been successful thus far and the process and findings have informed the aims of this renewal application. Being in a primary relationship is generally accepted as resulting in logistic and emotional support that provides health- promoting benefits. However, there is evidence that being in a primary relationship may result in behaviors, emotions, and conflict that may hinder adherence to prescribed treatment regimens. Framing our work in Social Control Theory while using dyadic data analysis and maintaining the couple as the unit of analysis will maximize our understanding of how couple interactions affect adherence. Our work to date has documented associations between partner dynamics and adherence and has suggested the importance of studying couples over time to best understand the dynamic interplay of relationship factors and ART adherence. We are therefore now proposing to extend the work through mixed qualitative, quantitative and randomized controlled trial (RCT) methodologies. The current Phase 3 study is a cross-sectional investigation of male couples to test hypotheses of the interrelationships among individual-level variables (e.g., beliefs about treatment efficacy, substance use, and adherence self-efficacy) and couple-level variables (e.g., relationship satisfaction, conflict, and adherence-specific partner support), and medication adherence and clinical variables. To optimize the contribution to the adherence and social relationship literature, we propose to follow these couples with repeat assessments at 6, 12, 18 and 24 months to test longitudinal hypotheses. We will purposefully select couples for in-depth qualitative interviews to further contextualize our findings and to inform interventions. Finally, we will develop and pilot a couples-based intervention, Duo PACT (Partnership Adherence Commitment Therapy), with 32 couples (equally randomized to intervention or assessment only control) to determine feasibility, satisfaction, and to inform effect size estimates for a larger trial of the intervention. Three well- validated self-report instruments will measure adherence to ART in all participants, and we will also use MEMS caps monitoring with those in the intervention to pilot procedures for a subsequent larger RCT. Clinical status will be assessed by ultrasensitive viral load and CD4 count assays. Significance. Findings will have clinical implications for the detection of adherence problems and the further development, evaluation, and dissemination of interventions to improve adherence within the couple relationship. Study findings will also have theoretical implications for the function of social control in the context of adherence to HIV medications within non-traditional relationships and across different serostatus configurations.